Dehydrofluorination of fluorohydrocarbons



United States Patent 3,235,609 DEHYDROFLUORINATION OF FLUOROHYDROCARBONS Maurice Stacye, Robert Stephens, and John Colin Tatlow, Birmingham, England, assignors to National Research Development Corporation, London, England, a British corporation No Drawing. Filed Mar. 11, 1963, Ser. No. 264,021 Claims priority, application Great Britain, Mar. 16, 1962, 10,286/ 62 6 Claims. (Cl. 260-648) This invention relates to the dehydrofluorination of fluorohydrocarbons.

Hitherto, fluorohydrocarbons, and particularly closed ring compounds, such as fluoro-butanes, -pentanes, -hexanes and hexenes, have been dehydrofluorinated by treatment with aqueous potassium hydroxide. Pyrolytic dehydrofluor-ination has also been proposed, but this has the disadvantage that, at the temperatures usually necessary to promote reasonable yields of the dehydrofluorinated product, the closed ring compounds tend to decompose. The present invention is based upon the discovery of an alternative method of dehydrofluorinating closed ring fluorohydrocarbons which is particularly eifective, which provides a synthetic route to compounds not obtainable by dehydrofluorination using aqueous potassium hydroxide and which can be carried out at temperatures substantially lower than are normally required for pyrolytic dehydrofiuorination.

According to the present invention, therefore, there is provided a process for the dehydrofluorination of closed ring fluorohydrocarbons selected from fluorocyclo-butanes, -pentanes, -hexanes and -hexenes which comprises contacting the fluorohydrocarbon with a heated metal fluoride whereby the dehydrofiuorination is promoted.

A convenient method of carrying out the process involves packing the metal fluoride in a tube and heating the tube whilst the fluorohydrocarbon is passed through it, preferably in a stream of inert gas such as nitrogen. The process is advantageously carried out under substantially anhydrous conditions.

The temperature to which the metal fluoride must be heated varies according to the fluorohydrocarbon treated, but it will normally be possible to obtain good yields at temperatures below 500 C. In many cases, a preferred working temperature will be in the range of 100 C. to 400 C., and particularly 300 to 400 C.

The metal fluoride is preferably a fluoride of a metal in Groups I, II or III of the Periodic Table. Alkali and alkaline earth metal fluorides especially sodium fluoride, are of particular importance, and aluminum fluoride is' also envisaged as being of use.

Besides promoting dehydrofluorination, the heated metal fluoride is capable of causing iso-merisation of the fluorohydrocaroon obtained as a result of the dehydrofluorination process, an effect which is not caused by aqueous potassium hydroxide and which is of the utmost import ance e.g. in the conversion of certain fluorocyclo-hexanes and hexenes to aromatic compounds. For instance, where a di-o-lefin containing vinylic hydrogen is a possible product of dehydrofluorination, as for example is the case in the dehydrofluorination of cis-3H/4H'octafluorocyclohexene, that product in the presence of heated metal fluoride will rearrange to a diene with allylic hydrogen and fluorine which immediately loses hydrogen fluoride to give a fluoro-aromatic compound The process of the invention as applied to fluorocyclohexanes and -hexenes thus provides a new synthetic route to fluoro-aromatic compounds.

It will be understood that the dehydrofluorination of a diene with allylic hydrogen and fluorine as mentioned 3,235,009 Patented Feb. 15, 1966 ICC EXAMPLES In theseexamples, reactions were carried out in horizontal tubes (preferably of metal though glass may be used it kept dry and at relatively low temperatures) heated electrically. The fluorohydrooarbons were introduced into the tube by slow evaporation in a stream of nitrogen.

Example 1 Undecafluorocyclohexane, C F H, B.P. 63 (9.0 g.), was passed over sodium fluoride pellets in a glass tube (temp. 320, nitrogen flow-rate 3 l./hr.) to give decafluorocyclohexene C F (6 g.) and unchanged undecafiuorocyclohexane (2.7 g.).

Example 2 Trans-lH/ZH-decafluorocyclohexane, C F H B.P. 79 (6.7 g.), was passed over sodium fluoride pellets in a glass tube (temp. 320", N flow-rate 3 1./hr.) to give octafiuorocyclohexa-l:4-diene (0.15 g.)*, octafluorocyclohexa-lzB-diene (0.15 g.), lH-nonafluorocyclohexene (2.25 g.), 3H-nonafluorocyclohexene (0.15 g.) and starting material (3.3 g.).

Example 3 Cis-lH/ZH-decafluorocyclohexane, C F H B.P. 91 (6.1 g.), was passed over sodium fluoride pellets in a glass tube (temp. 320, N flow-rate 3 l./ hr.) to give octafiuorocyclohexa-1:4-diene (0.15 g.)*, octafluorocyclohexa-lz3-diene (0.15 g.), lH-nonafluorocyclohexene (4.7 g.), 3H-nonafluorocyclohexene (0.3 g.) and starting material (0.3 g.).

Example 4 A mixture of trans-1H/3H- and trans-1H/4H-decafluorocyclohexanes, C F H B.P. 78 (6.0 g.), was passed over sodium fluoride pellets in a glass tube (temp. 320, N flow-rate 3 l./hr.) to give octafluorocyclohexa-l:4- diene (0.27 g.), octafluorocyclohexa-l:3-diene (0.54 g.), 4H-nonafluorocyclohexene (2.43 g.), 3H-nonaflu0rocyclohexene (1.08 g.) and a starting material (0.81 g.).

Example 5 Cis-lH,3H/-decafluorocyclohexane, C F H B.P. 89 (5.0 g.), was passed over sodium fluoride pellets in a glass tube (temp. 320, N flow-rate 3 l./hr.) to give octafluorocyclohexa-1z4-diene (0.4 g.), octafluorocyclohexa- 1:3-diene (1.4 g.), 4H-nonafluorocyclohexene (1.0 g.) and 3H-nonafluorocyclohexene (0.8 g.).

Example 6 Cis-3H,4H/-octafluorocyclohexene, C F H B.P. 116 (4.0 g.), was passed over sodium fluoride pellets in a glass tube (temp. 340, N flow-rate 3 l./ hr.) to give IH-heptafluorocyclohexa-1z4-diene (0.15 g.), lH-heptafluorocyclohexa-l:3-diene (0.15 g.), ZH-heptafluorocyclohexa-l:3- diene (0.3 g.) mixed 1H,2H-octafluorocyclohexene (0.65 g.) and hexafluorobenzene (0.65 g.) pentafluorobenzene 1.0 g.) and 1H,6H-octafluorocyclohexene (0.35 g.).

Example 7 Trans-4H/SH-octafluorocyclohexene, C F H B.P. (4.9 g.), was passed over sodium fluoride pellets in a glass *By an isomerisation of the 1 :3-diene.

tube (temp. 380, N flow-rate 3 l./-hr.) to give IH-heptafiuorocyclohexa-1z4-diene (0.35 g.), lH-heptafluorocycloheXa-1:3-diene (0.25 g.), ZH-heptafluorocyclohexad:3- diene (0.1 g.), mixed 1H,ZH-octafluorocyciohexene (0.65 g.), hexafluorobenzene (0.75 g.) containing a trace of trans-3H/4I-I octafluorocyclohexene, and .pentafluorobenzene (0.6 g.) containing a trace of starting material.

Compounds produced in accordance with the invention are useful intermediates in organic fluorine chemistry.

We claim:

1. Process for the production of a polyfluorocycloalkene compound which comprises dehydrofluorinating a polyfluorohydrocarbon selected from the group consisting of polyfluorocyclobutanes, polyfluorocycloipentanes, polyfluorocyclohexanes and polyflu-orocyclohexenes by bringing the latter into contact with sodium fluoride at a temperature between 100 and 500 C.

2. Process according to claim 1, in which the temperature is from 300 to 400 C. i

3. Process according to claim 2 in which the reaction References Cited by the Examiner FOREIGN PATENTS 619,394 3/1949 Great Britain.

OTHER REFERENCES Coe et a1.: Tetrahedronf .vol. 9, pp. 240-5, 1960.

LEON ZITVER, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,235,609 February 15, 1966 Maurice Stacey et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, line 1, and in the heading to the printed specification, line 4, for "Maurice Stacye", each occurrence, read Maurice Stacey r Signed and sealed this 31st day of January 1967.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. PROCES FOR THE PRODUCTION OF A POLYFLUOROCYCLOALKENE COMPOUND WHICH COMPRISES DEHYDROFLUORINATING A POLYFLUROHYDROCARBON SELECTED FROM THE GROUP CONSISTING OF POLYFLUOROCYCLOBUTANES, POLYFLUOROCYCLOPENTANES, POLYFLUOROCYCLOHEXANES AND POLYFLUOROCYCLOHEXENES OF BRINGING THE LATTER INTO CONTACT WITH SODIUM FLOURIDE AT A TEMPERATURE BETWEEN 100 AND 500*C. 